For a thin LSI chip, a technique of forming an integrated circuit and the like on a silicon substrate and then thinning the resultant structure from the lower surface side of the substrate using a grinder is known.
However, the integrated circuit and the like are formed only on the upper surface of the silicon substrate. Most parts are ground and wasted. Such a technique does not allow effectively using limited resources.
On the other hand, along with micropatterning and an increase in degree of integration of semiconductor devices, the chip heat density may greatly increase. Hence, there is an urgent need of establishing a technique for thin LSI chips.
A normal semiconductor chip itself has no flexibility. If it is to be mounted on a thin device such as an IC card, the bending strength must be increased. This is because a portable device such as an IC card may receive a bending force when it is accommodated. Hence, an LSI chip and the like which are mounted on a thin device must be thin from the viewpoint of heat dissipation and mechanical flexibility.
Japanese Patent Laid-Open No. 9-312349 describes a technique for a flexible LSI chip using separation by a porous layer.
More specifically, as shown in FIG. 6A, a device formation layer 10 is formed on a semiconductor substrate 11 via a porous layer 12. The device formation layer and holding substrate 16 are bonded via an adhesive 17. After that, an external force in a direction in which the semiconductor substrate 11 and holding substrate 16 are separated from each other is applied between the semiconductor substrate 11 and the holding substrate 16. Then, separation occurs at the mechanically weak porous layer 12, and the device formation layer 10 separates from the semiconductor substrate 11 together with the holding substrate 16 (FIG. 6B).
Next, a dicing film 18 that stretches when pulled in the planar direction is jointed to the rigid holding substrate 16 side. Dicing is performed using a dicing apparatus to form a kerf 19 from the device formation layer side (FIG. 6C). After that, the dicing film is stretched in the planar direction to separate chips. Thus, thin LSI chips are completed.
However, in the above thin LSI chip forming technique, since the separation step is executed using an external force, i.e., a tensile force, a strain may be partially locally applied to the semiconductor element and/or semiconductor integrated circuit which is formed in advance to adversely affect the device characteristics.